The proposed research is aimed at (1) further definition of the molecular mechanisms of deoxy-HbS polymerization, by studies of the role of non-S hemoglobins in polymerization, the effects of Hb dissociation equilibria and asymmetric hybrids in polymerization, and analysis of specific intermolecular contact sites in the polymer by correlating solution data with crystallographic data; (2) further studies of the functional properties of Hb-S containing red cells; and (3) expanded studies of the functional abnormalities of rbc membranes in hemoglobinopathic and other abnormal red cells. These include studies of the mechanism of dehydration of SS cells, by defining their abnormal ion transport properties, including transient activation of the Ca2+-sensitive K+-channel during sickling, the possible role of cell heterogeneity in Ca2+-sensitivity of K+ channels, diffusional chloride permeability, and alterations of Ca permeability and pump activity; the state of Ca in other abnormal rbc with high Ca contents, the role and mechanisms of formation and retention of endocytic vesicles; and interactions of Hb with the rbc membrane. Our methods will include studies of the polymer solubility of binary Hb mixtures under a variety of conditions, using tracer-labelled albumin as a marker of the nonpolymer phase; measurements of the ligand kinetics by stopped-flow techniques, and the hysteresis of sickling and rbc O2 equilibria of density-fractionated SS cells and SA red cells tonometered in plasma and physiological buffers; tracer flux studies of SS and other rbc with 45Ca, 86Rb, and other isotopes; monitoring of density distribution changes of rbc; comparative studies of cation and anion fluxes in SS and other rbc under physiological and experimental modeling conditions promoting dehydration; electron micrographic studies of endocytosis and identification of enclosed vesicles in rbc of splenectomized versus persons with spleen intact, in normal and hemolytic states; electron probe X-ray microanalyses of cryosections of rbc; and computer modeling of the kinetics of changes in rbc volume, pH and ionic composition under specified conditions, which can predict experimental testing of hypotheses about transport and volume regulation.